| Electronics > Projects, Designs, and Technical Stuff |
| How to use the same RELAY on 12V & 24V vehicles |
| << < (9/16) > >> |
| JDW:
--- Quote from: NiHaoMike on August 10, 2019, 05:00:51 am ---Since it's a small signal, have you considered an opto MOS solid state relay? --- Quote from: floobydust on August 09, 2019, 07:42:58 pm ---A reminder 24V vehicle electrical systems, especially trucks, are brutal. For 24V, the standard test is -600V, +200V spikes, so no off-the shelf Vreg can take it. --- End quote --- It's not that expensive to clamp those just like how kV level spikes are clamped on AC mains - use a MOV. --- End quote --- If you read through my previous relies, you will see I mention a TVS diode, which is a far better choice than MOV. I designed a switching power supply based on a Linear Technology (now Analog Devices) LTC3637 and a 1500W TVS diode with Vc=49.9V to cap spikes to less than the max Vin of 76V. It is designed for exclusive use on 24V trucks, which is why my design is based on their example 12.5V-76V design presented in the datasheet. My design actually works on 12V too, but the average current consumption is too high to make it a good choice on passenger cars. The LTC3637 is also an expensive chip too, which is why I am considered TI chips for this new design I am working on now. |
| soldar:
--- Quote from: floobydust on August 10, 2019, 12:47:12 am --- OT Cassette-player brushed DC motors use either internal centrifugal switches, voltage regulator, or a tachogenerator+transistor/IC for speed control. I worked in a repair shop and have seen 100's of them. The capstan flywheel deal's with flutter. The point is constant current control is not used in them. --- End quote --- I appreciate your experience and knowledge but don't say something was never done just because you haven't seen it done. It may be that American/Japanese industry favored different solutions than European industry. I have no doubt that as time advanced better solutions were developed with ICs, tachos, etc. but I was thinking of units I repaired which dated to the late 1960's and probably did not have even silicon transistors, let alone ICs. Everything was as basic as you could get. They were Spanish made but might have been knock offs of better brands like Philips. I distinctly remember encountering that circuit and thinking it was ingenious. I can't see why it would not work. Varying only the input voltage and maintaining the load constant the current and voltage should remain constant. At any rate, I do not want to hijack this thread any further with this topic so that's my last word on this topic. --- Quote from: floobydust on August 10, 2019, 12:47:12 am --- 6W is an awful lot of heat, just pick out a heatsink and you will see it needs to be huge. I haven't seen a relay with 24R coil and 0.5A coil current- for another 6W, it's pretty big too. So I thought it's a circuit that could work but the example's details are coffee warmer kind of hot and made me cringe. You could do it with one transistor as the MCU's output voltage is stable at 3.3V for CC control. --- End quote --- It seems to me you are looking to argue for the sake of arguing. The circuit I showed will allow a 12 V relay to work at 12 and at 24 V and when working at 24 V will dissipate the same heat as the relay, whatever that is. If you want to argue a vehicle can only activate one relay at a time because the heat of two relays would overheat the vehicle ... well, that's just silly. Again, as I said when I showed it, it is a simple circuit, quick and dirty, and it works. Criticizing it for being simple, quick and dirty is silly and criticizing it for dissipating as much as the relay it is controlling is double silly. A vehicle has many relays and the heat they produce is insignificant compared to other sources of heat in the vehicle. Any vehicle, at any one time, is dissipating in heat produced by electrical items hundreds of watts and the heat produced by a relay or two is just insignificant. Even more so if the relay is activated for a very short time. And that's my last word on this issue. |
| Zero999:
--- Quote from: soldar on August 10, 2019, 10:10:19 am --- --- Quote from: floobydust on August 10, 2019, 12:47:12 am --- OT Cassette-player brushed DC motors use either internal centrifugal switches, voltage regulator, or a tachogenerator+transistor/IC for speed control. I worked in a repair shop and have seen 100's of them. The capstan flywheel deal's with flutter. The point is constant current control is not used in them. --- End quote --- I appreciate your experience and knowledge but don't say something was never done just because you haven't seen it done. It may be that American/Japanese industry favored different solutions than European industry. I have no doubt that as time advanced better solutions were developed with ICs, tachos, etc. but I was thinking of units I repaired which dated to the late 1960's and probably did not have even silicon transistors, let alone ICs. Everything was as basic as you could get. They were Spanish made but might have been knock offs of better brands like Philips. I distinctly remember encountering that circuit and thinking it was ingenious. I can't see why it would not work. Varying only the input voltage and maintaining the load constant the current and voltage should remain constant. At any rate, I do not want to hijack this thread any further with this topic so that's my last word on this topic. --- Quote from: floobydust on August 10, 2019, 12:47:12 am --- 6W is an awful lot of heat, just pick out a heatsink and you will see it needs to be huge. I haven't seen a relay with 24R coil and 0.5A coil current- for another 6W, it's pretty big too. So I thought it's a circuit that could work but the example's details are coffee warmer kind of hot and made me cringe. You could do it with one transistor as the MCU's output voltage is stable at 3.3V for CC control. --- End quote --- It seems to me you are looking to argue for the sake of arguing. The circuit I showed will allow a 12 V relay to work at 12 and at 24 V and when working at 24 V will dissipate the same heat as the relay, whatever that is. If you want to argue a vehicle can only activate one relay at a time because the heat of two relays would overheat the vehicle ... well, that's just silly. Again, as I said when I showed it, it is a simple circuit, quick and dirty, and it works. Criticizing it for being simple, quick and dirty is silly and criticizing it for dissipating as much as the relay it is controlling is double silly. A vehicle has many relays and the heat they produce is insignificant compared to other sources of heat in the vehicle. Any vehicle, at any one time, is dissipating in heat produced by electrical items hundreds of watts and the heat produced by a relay or two is just insignificant. Even more so if the relay is activated for a very short time. And that's my last word on this issue. --- End quote --- He is right. Delivering a constant current to a permanent magnet DC motor will not result in a constant speed, but a constant torque. Voltage regulation is required to achieve a constant speed. Even if you're wrong about the original application of the circuit, you're right that it is suitable for enabling a 12V relay to work with either 12V or 24V. |
| soldar:
--- Quote from: Zero999 on August 10, 2019, 12:52:44 pm --- He is right. Delivering a constant current to a permanent magnet DC motor will not result in a constant speed, but a constant torque. Voltage regulation is required to achieve a constant speed. Even if you're wrong about the original application of the circuit, you're right that it is suitable for enabling a 12V relay to work with either 12V or 24V. --- End quote --- Would constant torque with a constant load result in constant speed? Most or all turntables I have had worked with shaded pole motors which will slow down with increasing load but the variability of the load was so insignificant that it was considered constant. I think it would be the same with the capstan of a cassette player. The load would be pretty much constant . |
| Zero999:
--- Quote from: soldar on August 10, 2019, 01:09:31 pm --- --- Quote from: Zero999 on August 10, 2019, 12:52:44 pm --- He is right. Delivering a constant current to a permanent magnet DC motor will not result in a constant speed, but a constant torque. Voltage regulation is required to achieve a constant speed. Even if you're wrong about the original application of the circuit, you're right that it is suitable for enabling a 12V relay to work with either 12V or 24V. --- End quote --- Would constant torque with a constant load result in constant speed? Most or all turntables I have had worked with shaded pole motors which will slow down with increasing load but the variability of the load was so insignificant that it was considered constant. I think it would be the same with the capstan of a cassette player. The load would be pretty much constant . --- End quote --- Interesting point. I don't know whether the load would be constant or not. I would have thought that a turntable would have more friction when the stylus is on the outside and less when it's in the middle. |
| Navigation |
| Message Index |
| Next page |
| Previous page |